In the mobile communication system, a transmitted electric power control technique has been usually known that transmitted electric power is controlled in accordance with a distance between a base station and a mobile station when information is transmitted to make the electric power of a signal received by the base station constant, suppress an interference between communication channels and improve a frequency using efficiency.
Especially, in a mobile communication system of a CDMA (Code Division Multiple Access) system using a spectrum diffusion technique for multiplexing a plurality of communication channels, the same frequency and the same time are shared between users. Accordingly, when the transmitted electric power from the mobile station is the same irrespective of a distance from the base station or a transmitting environment, a problem related to near or remote places undesirably arises that a signal from a near place is strong and a signal from a remote mobile station cannot be separated.
Therefore, to properly demodulate respective signal waves by an inverse diffusion in the base station, the receiving levels of the signal waves respectively need to be made uniform and a high electric power control is necessary in the mobile station. Specially, in the CDMA system, a wide dynamic range or a high linearity is required. Particularly, in the CDMA system of a broad band (W-CDMA or the like), the accuracy of transmitted electric power is highly required upon large electric power.
A usual radio communication device includes, as shown in FIG. 7, an antenna 1 for transmitting and receiving a radio signal and a transmit and receive separator 2 for separating a transmitting signal from a receiving signal. A receiving system comprises a radio receiving part 3 having a high frequency amplifying circuit for high-frequency amplifying the receiving signal and outputting an IF signal with a frequency converted to an IF (intermediate frequency) band, a local oscillating circuit and an IF signal amplifying circuit or the like, a demodulator 4 for converting the receiving signal to a base band signal and a base band signal processing part 5 for carrying out a signal process and a decoding process of the received base band signal.
Further, a transmitting system comprises the base band signal processing part 5 for carrying out a signal process and an encoding process of a transmitted base band signal, a modulator 13 for modulating the transmitting signal and outputting the IF signal and a radio transmitting part 14 for amplifying the electric power of the transmitting signal and converting a frequency to an RF (radio frequency) band. Further, the radio transmitting part 14 has a variable gain amplifier 15.
Further, in the radio communication device, a transmitted electric power control system includes the base band signal processing part 5, a transmitted electric power setting part 6 for receiving a transmitted electric power control bit outputted from the base band signal processing part 5 to set a transmitted electric power and an electric power value/gain control signal converting part 8 for converting a transmitted electric power setting value from the transmitted electric power setting part 6 to a gain control signal.
Further, a radio communication device having a transmitted electric power correcting function includes, as a transmitted electric power adjusting system, a transmitted electric power detecting part 9 for detecting transmitted electric power radiated from the antenna 1 to output a detecting signal, an error calculating part 10 for comparing the detecting signal with a gain control signal to calculate an error between the detecting signal and the gain control signal and output an error signal and an adding part 12 for adding the error signal to the gain control signal.
In the above-described usual structure, the transmitted electric power control bit is extracted on the basis of the base band signal obtained by demodulating the receiving signal to obtain the transmitted electric power setting value on the basis of the transmitted electric power control bit and convert the transmitted electric power setting value to the gain control signal A. On the other hand, the output value of the transmitted electric power radiated from the antenna 1 is detected. An error between the transmitted electric power instructed by the transmitted electric power control bit and actually transmitted electric power is detected as an error signal from the detecting signal corresponding to the transmitted electric power output value and the gain control signal A. This error signal is added to the gain control signal A to generate a gain control signal B. A transmitted electric power gain is controlled by the gain control signal B so that the error signal becomes zero in a closed loop. Thus, the accuracy of the transmitted electric power is improved. That is, the transmitted electric power setting value is compared with the transmitted electric power output value and the calculated error signal is added to the control signal so the feedback control of the transmitted electric power is carried out.
However, the detecting characteristics of a detecting diode of the transmitted electric power detecting part 9 show that the change of detecting voltage is small within a range in which the transmitted electric power is low as shown in FIG. 8. Accordingly, the transmitted electric power detecting part that meets a wide dynamic range necessary for the CDMA system is hardly realized. Accordingly, a control for operating a transmitted electric power control may be considered only upon large electric power that needs a high accuracy of the transmitted electric power. In the above-described usual technique, during the closed loop control that the transmitted electric power is relatively variably controlled, when a variable control exceeding the operating threshold value of a transmitted electric power control is carried out, the error signal (error voltage) outputted from the error calculating part abruptly changes. Therefore, an error is undesirably generated in a relative value and an accuracy of the transmitted electric power control is undesirably deteriorated.
The present invention is proposed to solve the above-described usual problems and it is an object of the present invention to provide a radio communication device that can suppress an abrupt gain change and smoothly and highly accurately control transmitted electric power even if the transmitted electric power crosses the threshold value to change when a closed loop control is performed to cross the threshold value as the detection limit of the transmitted electric power.